Antioxidant vitamin E protects embryos of Xenopus tropicalis against lambda-cyhalothrin induced embryotoxicity.

Pesticides are capable of increasing risks to the early development of nontarget organisms through oxidative stress. The supplementation of antioxidants could help to modulate the toxic effects of pesticides, but much remains to be understood in the interactions between pesticides and antioxidants in amphibians. In the present study, the embryotoxicity of a widely used pyrethroid, lambda-cyhalothrin (LCT), and the potential effect of α-tocopherol (TOC) on embryos of Xenopus tropicalis were evaluated. Exposure to LCT did not affect the hatch rate, survival, or body length of the embryos. However, environmentally relevant concentrations of LCT could induce significant malformations on the larvae. Exposure to LCT led to a concentration-dependent induction of oxidative stress and cytotoxicity that subsequently resulted in embryotoxicity. During the early developmental stages, vitamin E could work as a powerful protective antioxidant. The LCT-induced overproduction of reactive oxygen species and increased enzymatic activities were fully inhibited by treatment with 1 µg/L TOC. However, only supplementation with 100 µg/L TOC provided partial protection against the morphological changes caused by LCT. The results from the present study suggest that antioxidant vitamin E possesses protective potential against pyrethroid-induced embryotoxicity in amphibian embryos through the prevention of oxidative stress.

Effects of hyperthyroidism in the development of the appendicular skeleton and muscles of zebrafish, with notes on evolutionary developmental pathology (Evo-Devo-Path).

The hypothalamus-pituitary-thyroid (HPT) axis plays a crucial role in the metabolism, homeostasis, somatic growth and development of teleostean fishes. Thyroid hormones regulate essential biological functions such as growth and development, regulation of stress, energy expenditure, tissue compound, and psychological processes. Teleost thyroid follicles produce the same thyroid hormones as in other vertebrates: thyroxin (T4) and triiodothyronine (T3), making the zebrafish a very useful model to study hypo- and hyperthyroidism in other vertebrate taxa, including humans. Here we investigate morphological changes in T3 hyperthyroid cases in the zebrafish to better understand malformations provoked by alterations of T3 levels. In particular, we describe musculoskeletal abnormalities during the development of the zebrafish appendicular skeleton and muscles, compare our observations with those recently done by us on the normal developmental of the zebrafish, and discuss these comparisons within the context of evolutionary developmental pathology (Evo-Devo-Path), including human pathologies.

Overexpression of Human Mutant PANK2 Proteins Affects Development and Motor Behavior of Zebrafish Embryos.

Pantothenate Kinase-Associated Neurodegeneration (PKAN) is a genetic and early-onset neurodegenerative disorder characterized by iron accumulation in the basal ganglia. It is due to mutations in Pantothenate Kinase 2 (PANK2), an enzyme that catalyzes the phosphorylation of vitamin B5, first and essential step in coenzyme A (CoA) biosynthesis. Most likely, an unbalance of the neuronal levels of this important cofactor represents the initial trigger of the neurodegenerative process, yet a complete understanding of the connection between PANK2 malfunctioning and neuronal death is lacking. Most PKAN patients carry mutations in both alleles and a loss of function mechanism is proposed to explain the pathology. When PANK2 mutants were analyzed for stability, dimerization capacity, and enzymatic activity in vitro, many of them showed properties like the wild-type form. To further explore this aspect, we overexpressed the wild-type protein, two mutant forms with reduced kinase activity and two retaining the catalytic activity in zebrafish embryos and analyzed the morpho-functional consequences. While the wild-type protein had no effects, all mutant proteins generated phenotypes that partially resembled those observed in pank2 and coasy morphants and were rescued by CoA and vitamin B5 supplementation. The overexpression of PANK2 mutant forms appears to be associated with perturbation in CoA availability, irrespective of their catalytic activity.

The folic acid metabolism gene mel-32/Shmt is required for normal cell cycle lengths in Caenorhabditis elegans.

Neural tube defects are common and serious birth defects in which the brain and/or spinal cord are exposed outside the body. Supplementation of foods with folic acid, an essential vitamin, is linked to a lower risk of neural tube defects; however, the mechanisms by which folic acid influence neural tube defect risk are unclear. Our research seeks to identify the basic cellular roles of known folic acid metabolism genes during morphogenesis using the roundworm Caenorhabditis elegans (C. elegans) as a simple model system. Here, we used live imaging to characterize defects in embryonic development when mel-32 is depleted. mel-32 is an essential folic acid metabolism gene in C. elegans and a homolog to the mammalian enzyme serine hydroxymethyltransferase (Shmt). Disruption of mel-32 resulted in a doubling or tripling of cell cycle lengths and a lack of directed cell movement during embryogenesis. However, the order of cell divisions, as determined by lineage analysis, is unchanged compared to wild type embryos. These results suggest that mel-32/Shmt is required for normal cell cycle lengths in C. elegans.

Effects of Essential Oil from Thymus vulgaris on Viability and Inflammation in Zebrafish Embryos.

Innate immunity provides the initial response against pathogens and includes the inflammatory response. Regulation of the initiation and duration of neutrophil and mononuclear cell influx during inflammation determines both the successfulness of pathogen elimination and the level of resulting tissue damage. Zebrafish embryos provide excellent opportunities to visualize the inflammatory response. Neutrophil granules may be stained with Sudan black, and variation in neutrophil counts may be used to monitor the level of the response. Inflammation may be triggered by injuring the caudal fin, providing an opportunity for testing possible anti-inflammatory compounds in a whole-animal system. The use of homeopathic compounds as anti-inflammatory treatments is common in alternative medicine. Effects of unfractionated essential oil from Thymus vulgaris and its specific component, carvacrol, have been examined in cells in culture and in rodents. Our work extends this research to zebrafish, and includes toxicity and morphological studies as well as examination of anti-inflammatory effects following tail fin injury. Our results show that zebrafish are more sensitive to thyme oil compared to cells in culture, that cardiac defects arise due to thyme oil treatment, and that thyme oil reduces neutrophil infiltration during an inflammatory response.

Molecular Mechanisms of Crude Oil Developmental Toxicity in Fish.

With major oil spills in Korea, the United States, and China in the past decade, there has been a dramatic increase in the number of studies characterizing the developmental toxicity of crude oil and its associated polycyclic aromatic compounds (PACs). The use of model fish species with associated tools for genetic manipulation, combined with high throughput genomics techniques in nonmodel fish species, has led to significant advances in understanding the cellular and molecular bases of functional and morphological defects arising from embryonic exposure to crude oil. Following from the identification of the developing heart as the primary target of crude oil developmental toxicity, studies on individual PACs have revealed a diversity of cardiotoxic mechanisms. For some PACs that are strong agonists of the aryl hydrocarbon receptor (AHR), defects in heart development arise in an AHR-dependent manner, which has been shown for potent organochlorine agonists, such as dioxins. However, crude oil contains a much larger fraction of compounds that have been found to interfere directly with cardiomyocyte physiology in an AHR-independent manner. By comparing the cellular and molecular responses to AHR-independent and AHR-dependent toxicity, this review focuses on new insights into heart-specific pathways underlying both acute and secondary adverse outcomes to crude oil exposure during fish development.

Molecular mechanisms of selenium-Induced spinal deformities in fish.

Selenium toxicity to oviparous vertebrates is often attributed to selenomethionine (SeMet), which can biomagnify through maternal transfer. Although oxidative stress is implicated in SeMet toxicity, knowledge gaps remain in how SeMet causes characteristic spinal deformities. In the present study, we use the Japanese medaka (Oryzias latipes) model to investigate the role of oxidative stress, cell death, and the unfolded protein response (UPR) on skeletal gene expression and SeMet toxicity, linking localization of cellular effects to observed abnormalities. Medaka embryos were treated with 2.5µM or 5µM SeMet for 24h at stage 25 (48h post fertilization). Post treatment, embryos were separated into normal, deformed (mild, moderate or severe), or dead categories. Dichlorofluorescein staining demonstrated oxidative stress in tails of embryos with observable spinal malformations. Furthermore, acridine orange staining for apoptosis identified significantly more dead cells in tails of treated embryos. Gene expression studies for the UPR suggest a potential role for CHOP (c/ebp homologous protein) induced apoptosis deformed embryos after 5µM SeMet, accompanied by a significant decrease in PDIA4 (protein disulfide isomerase A4) and no change in Dnajb9 (ER DNA J Domain-Containing Protein 4). This expression was distinct from the UPR induced by well-studied ER stress inducer, tunicamycin, which robustly activated CHOP, PDIA4 and Dnajb9. Finally, SeMet treatment significantly decreased transcripts of cartilage development, Sox9 (SRY box 9), while increasing Runx2 in deformed embryos, without altering Twist or Collagen 2a1. Results suggest that oxidative stress, the UPR and cell death play key roles in SeMet induced deformities and altered skeletal development factors.

Chemical Screening in Zebrafish.

Phenotypic small molecule screens in zebrafish have gained popularity as an unbiased approach to probe biological processes. In this chapter we outline basic methods for performing chemical screens with larval zebrafish including breeding large numbers of embryos, plating larval fish into multi-well dishes, and adding small molecules to these wells. We also highlight important considerations when designing and interpreting the results of a phenotypic screen and possible follow-up approaches, including popular methods used to identify the mechanism of action of a chemical compound.

Parental dietary seleno-L-methionine exposure and resultant offspring developmental toxicity.

Selenium (Se) leaches into water from agricultural soils and from storage sites for coal fly ash. Se toxicity causes population and community level effects in fishes and birds. We used the laboratory aquarium model fish, Japanese medaka (Oryzias latipes), an asynchronous breeder, to determine aspects of uptake in adults and resultant developmental toxicity in their offspring. The superior imaging properties of the model enabled detailed descriptions of phenotypic alterations not commonly reported in the existing Se literature. Adult males and females in treatment groups were exposed, separately and together, to a dry diet spiked with 0, 12.5, 25, or 50 µg/g (dry weight) seleno-L-methionine (SeMet) for 6 days, and their embryo progeny collected for 5 days, maintained under controlled conditions and observed daily for hatchability, mortality and/or developmental toxicity. Sites of alteration included: craniofacial, pericardium and abdomen (Pc/Ab), notochord, gall bladder, spleen, blood, and swim bladder. Next, adult tissue Se concentrations (liver, skeletal muscle, ovary and testis) were determined and compared in treatment groups of bred and unbred individuals. No significant difference was found across treatment groups at the various SeMet concentrations; and, subsequent analysis compared exposed vs. control in each of the treatment groups at 10 dpf. Increased embryo mortality was observed in all treatment groups, compared to controls, and embryos had a decreased hatching rate when both parents were exposed. Exposure resulted in significantly more total altered phenotypes than controls. When altered phenotypes following exposure of both parents were higher than maternal only exposure, a male role was suggested. The comparisons between treatment groups revealed that particular types of phenotypic change may be driven by the sex of the exposed parent. Additionally, breeding reduced Se concentrations in some adult tissues, specifically the liver of exposed females and skeletal muscle of exposed males. Detailed phenotypic analysis of progeny from SeMet exposed parents should inform investigations of later life stages in an effort to determine consequences of early life exposure.

Bioelectric memory: modeling resting potential bistability in amphibian embryos and mammalian cells.

BACKGROUND: Bioelectric gradients among all cells, not just within excitable nerve and muscle, play instructive roles in developmental and regenerative pattern formation. Plasma membrane resting potential gradients regulate cell behaviors by regulating downstream transcriptional and epigenetic events. Unlike neurons, which fire rapidly and typically return to the same polarized state, developmental bioelectric signaling involves many cell types stably maintaining various levels of resting potential during morphogenetic events. It is important to begin to quantitatively model the stability of bioelectric states in cells, to understand computation and pattern maintenance during regeneration and remodeling. METHOD: To facilitate the analysis of endogenous bioelectric signaling and the exploitation of voltage-based cellular controls in synthetic bioengineering applications, we sought to understand the conditions under which somatic cells can stably maintain distinct resting potential values (a type of state memory). Using the Channelpedia ion channel database, we generated an array of amphibian oocyte and mammalian membrane models for voltage evolution. These models were analyzed and searched, by simulation, for a simple dynamical property, multistability, which forms a type of voltage memory. RESULTS: We find that typical mammalian models and amphibian oocyte models exhibit bistability when expressing different ion channel subsets, with either persistent sodium or inward-rectifying potassium, respectively, playing a facilitative role in bistable memory formation. We illustrate this difference using fast sodium channel dynamics for which a comprehensive theory exists, where the same model exhibits bistability under mammalian conditions but not amphibian conditions. In amphibians, potassium channels from the Kv1.x and Kv2.x families tend to disrupt this bistable memory formation. We also identify some common principles under which physiological memory emerges, which suggest specific strategies for implementing memories in bioengineering contexts. CONCLUSION: Our results reveal conditions under which cells can stably maintain one of several resting voltage potential values. These models suggest testable predictions for experiments in developmental bioelectricity, and illustrate how cells can be used as versatile physiological memory elements in synthetic biology, and unconventional computation contexts.

A high-throughput method for predicting drug effects on gut transit time using larval zebrafish.

INTRODUCTION: Zebrafish are an attractive vertebrate model due to their small size, transparency through organogenesis, and high fecundity. The zebrafish gastrointestinal (GI) tract is similar to the mammalian GI tract in gene expression, nervous system control, and response to chemical challenges. GI intolerance is a common preclinical finding and can be a serious clinical safety concern. Mammalian GI liability tests are conducted at the expense of time, test article, and labor. We developed a high-throughput method to predict mammalian GI safety issues using larval zebrafish. METHODS: Fluorescent food is fed to larval zebrafish (7 days post fertilization). After feeding, larvae are placed individually into wells of a 96-well plate and dosed with test compounds. Fluorescence is measured from the bottom of the wells repeatedly over the course of 24h and thus fecal accumulation is tracked over time. The area under the curve is compared between treated and vehicle-treated groups. RESULTS: Drugs with established clinical GI effects significantly impacted zebrafish GI transit time as measured by this method; tegaserod and metoclopramide accelerated transit time, while atropine and amitriptyline slowed transit time. This method is sensitive enough to reflect dose-level associated effects as demonstrated using atropine. Using a suite of 24 compounds with known (positive or negative) mammalian GI effects, we characterized this method as having a high positive predictive value. DISCUSSION: Here we present an efficient assay for predicting mammalian GI transit liabilities using larval zebrafish. With this assay, an investigator can evaluate dozens of compounds in a single day using very little amount of each test article. As such, safe drug candidates can be prioritized for mammalian testing, which expedites the discovery process and provides 3 Rs impact.

Combined effects of depleted uranium and ionising radiation on zebrafish embryos.

In the environment, living organisms are exposed to a mixture of stressors, and the combined effects are deemed as multiple stressor effects. In the present work, the authors studied the multiple stressor effect in embryos of the zebrafish (Danio rerio) from simultaneous exposure to alpha particles and depleted uranium (DU) through quantification of apoptotic signals at 24 h post-fertilisation (hpf) revealed by vital dye acridine orange staining. In each set of experiments, dechorionated zebrafish embryos were divided into 4 groups, each having 10 embryos: Group (C) in which the embryos did not receive any further treatment; Group (IU) in which the embryos received an alpha-particle dose of 0.44 mGy at 5 hpf and were then exposed to 100 µg l(-1) of DU from 5 to 6 hpf; Group (I) in which the embryos received an alpha-particle dose of 0.44 mGy at 5 hpf and Group (U) in which the dechorionated embryos were exposed to 100 µg l(-1) of DU from 5 to 6 hpf. The authors confirmed that an alpha-particle dose of 0.44 mGy and a DU exposure for 1 h separately led to hormetic and toxic effects assessed by counting apoptotic signals, respectively, in the zebrafish. Interestingly, the combined exposure led to an effect more toxic than that caused by the DU exposure alone, so effectively DU changed the beneficial effect (hormesis) brought about by alpha-particle irradiation into an apparently toxic effect. This could be explained in terms of the promotion of early death of cells predisposed to spontaneous transformation by the small alpha-particle dose (i.e. hormetic effect) and the postponement of cell death upon DU exposure.

Acute embryonic or juvenile exposure to Deepwater Horizon crude oil impairs the swimming performance of mahi-mahi (Coryphaena hippurus).

The Deepwater Horizon incident likely resulted in exposure of commercially and ecologically important fish species to crude oil during the sensitive early life stages. We show that brief exposure of a water-accommodated fraction of oil from the spill to mahi-mahi as juveniles, or as embryos/larvae that were then raised for ∼25 days to juveniles, reduces their swimming performance. These physiological deficits, likely attributable to polycyclic aromatic hydrocarbons (PAHs), occurred at environmentally realistic exposure concentrations. Specifically, a 48 h exposure of 1.2 ± 0.6 µg L(-1) ΣPAHs (geometric mean ± SEM) to embryos/larvae that were then raised to juvenile stage or a 24 h exposure of 30 ± 7 µg L(-1) ΣPAHs (geometric mean ± SEM) directly to juveniles resulted in 37% and 22% decreases in critical swimming velocities (Ucrit), respectively. Oil-exposed larvae from the 48 h exposure showed a 4.5-fold increase in the incidence of pericardial and yolk sac edema relative to controls. However, this larval cardiotoxicity did not manifest in a reduced aerobic scope in the surviving juveniles. Instead, respirometric analyses point to a reduction in swimming efficiency as a potential alternative or contributing mechanism for the observed decreases in Ucrit.

Optimization protocol for storage of goldfish (Carassius auratus) embryos in chilled state.

A series of five experiments were conducted to explore suitable conditions for storing of goldfish embryos in a chilled state. The factors studied were embryo stage, storage temperature, physiological saline solutions and goldfish artificial coelomic fluid (GFACF) medium, antibiotics (penicillin and streptomycin), antioxidants (vitamin E, vitamin C), buffer (Hepes, Tris) and BSA (bovine serum albumin). First, goldfish embryos at eight developmental stages were incubated in aerated and dechlorinated tap water at 0 °C for 24 h. Result shows that early developmental stages were most sensitive to chilling. Heartbeat-stage goldfish embryos were chilled at 0, 4 or 8 °C for up to 72 h in water, and chilled storage was possible only for up to 18, 24 and 48 h at 0, 4 and 8 °C, respectively, without a decrease in viability. Chilling of goldfish embryos at 8 °C in GFACF medium and Dettlaff's solution instead of water and other physiological saline solutions prolonged their viability (p < 0.01). Nevertheless, viability of chilled embryos in GFACF medium was slightly, but non-significantly, higher than in Dettlaff's solution. Supplementation of the GFACF medium with antibiotics, Hepes or BSA increased the viability of chilled embryos, but the tested vitamin E analogue Trolox, vitamin C or Tris concentration had no effect on embryo viability. The outcome of this series of experiments shows that heartbeat-stage goldfish embryos could be chilled for 60 h in GFACF supplemented with 25 mm Hepes, 100 U/ml penicillin, 10 µg/l streptomycin and 1 g/l BSA in such a way that embryonic development does not proceed, and viability is not lost.

Zebrafish embryos/larvae for rapid determination of effects on hypothalamic-pituitary-thyroid (HPT) and hypothalamic-pituitary-interrenal (HPI) axis: mRNA expression.

To identify and prioritize chemicals that may affect thyroid and adrenal/interregnal endocrine system and to reduce cost and animal use by conventional toxicity assay, an in vivo screening assay was developed using zebrafish embryos/larvae based on measurement of expression of genes that were suggested to play important roles in hypothalamic-pituitary-thyroid (HPT) and hypothalamic-pituitary-interrenal (HPI) axis. Model chemicals that could modulate HPT and HPI axis in adult fish were selected in assay validation, including anti-thyroid agent 6-Propyl-2-thiouracil (PTU) and cytochrome P450 11B (Cyp11b) enzyme inhibitor metyrapone (MET). Zebrafish embryos were exposed to different concentrations of model chemical from 4h post-fertilization (hpf) to 5d post-fertilization (dpf). Exposure to PTU increased mRNA expression of sodium iodide symporter (nis) and thyroglobulin (tg) involved in HPT axis, and MET treatment up-regulated all the mRNA expression tested involved in HPI axis by a compensatory mechanism. These results suggested that HPT and HPI axis were active upon chemical exposure at least at 5 dpf zebrafish. Furthermore, we studied the effects of PTU or MET on the cross-talk between HPT and HPI axis. The results demonstrated that PTU and MET could affect cross-talk responses in zebrafish embryos/larvae.

Chemical genetics and drug discovery in Xenopus.

Chemical genetics uses small molecules to modulate protein function and has the potential to perturb any biochemical event in a complex cellular context. The application of chemical genetics to dissect biological processes has become an attractive alternative to mutagenesis screens due to its technical simplicity, inexpensive reagents, and low-startup costs. Xenopus embryos are particularly amenable to whole organism chemical genetic screens. Here we describe the basic protocols we have developed to screen small compound libraries on Xenopus laevis embryos. We score embryos either by observing phenotypic changes in the whole tadpole or by changes in gene expression pattern using automated wholemount in situ hybridization.

A novel zebrafish model of hyperthermia-induced seizures reveals a role for TRPV4 channels and NMDA-type glutamate receptors.

Febrile seizures are the most common seizure type in children under the age of five, but mechanisms underlying seizure generation in vivo remain unclear. Animal models to address this issue primarily focus on immature rodents heated indirectly using a controlled water bath or air blower. Here we describe an in vivo model of hyperthermia-induced seizures in larval zebrafish aged 3 to 7 days post-fertilization (dpf). Bath controlled changes in temperature are rapid and reversible in this model. Acute electrographic seizures following transient hyperthermia showed age-dependence, strain independence, and absence of mortality. Electrographic seizures recorded in the larval zebrafish forebrain were blocked by adding antagonists to the transient receptor potential vanilloid (TRPV4) channel or N-methyl-d-aspartate (NMDA) glutamate receptor to the bathing medium. Application of GABA, GABA re-uptake inhibitors, or TRPV1 antagonist had no effect on hyperthermic seizures. Expression of vanilloid channel and glutamate receptor mRNA was confirmed by quantitative PCR analysis at each developmental stage in larval zebrafish. Taken together, our findings suggest a role of heat-activation of TRPV4 channels and enhanced NMDA receptor-mediated glutamatergic transmission in hyperthermia-induced seizures.

Chemical screening in zebrafish for novel biological and therapeutic discovery.

Zebrafish chemical screening allows for an in vivo assessment of small molecule modulation of biological processes. Compound toxicities, chemical alterations by metabolism, pharmacokinetic and pharmacodynamic properties, and modulation of cell niches can be studied with this method. Furthermore, zebrafish screening is straightforward and cost-effective. Zebrafish provide an invaluable platform for novel therapeutic discovery through chemical screening.

Designing zebrafish chemical screens.

The zebrafish is proving to be highly amenable to in vivo small molecule screening. With a growing number of screens successfully completed, a rich interface is being created between disciplines that have historically used zebrafish (e.g., embryology and genetics) and disciplines focused on small molecules (e.g., chemistry and pharmacology). Navigating this interface requires consideration of the unique demands of conducting high-throughput screening in vivo. In this chapter, we discuss design elements of successful zebrafish screens, established screening methods, and approaches for mechanism of action studies following discovery of novel small molecules. These methods are enabling the zebrafish to have an increasingly positive impact on biomedical research and drug development.

Using the zebrafish photomotor response for psychotropic drug screening.

Because psychotropic drugs affect behavior, we can use changes in behavior to discover psychotropic drugs. The original prototypes of most neuroactive medicines were discovered in humans, rodents and other model organisms. Most of these discoveries were made by chance, but the process of behavior based drug discovery can be made more systematic and efficient. Fully automated platforms for analyzing the behavior of embryonic zebrafish capture digital video recordings of animals in each individual well of a 96-well plate before, during, and after a series of stimuli. To analyze systematically the thousands of behavioral recordings obtained from a large-scale chemical screen, we transform these behavioral recordings into numerical barcodes, providing a concise and interpretable summary of the observed phenotypes in each well. Systems-level analysis of these behavioral phenotypes generate testable hypotheses about the molecular mechanisms of poorly understood drugs and behaviors. By combining the in vivo relevance of behavior-based phenotyping with the scale and automation of modern drug screening technologies, systematic behavioral barcoding represents a means of discovering psychotropic drugs and provides a powerful, systematic approach for unraveling the complexities of vertebrate behavior.